GridView and DropDownlist - asp.net

Question

I have a gridview that when enter to edit mode one of the column change to dropdownlist:
<EditItemTemplate>
<asp:DropDownList ID="DropDownList2" runat="server"
DataSourceID="SqlDataSource1" DataTextField="name" DataValueField="name">
</asp:DropDownList>
</EditItemTemplate>
Now i have a SqlDataSource with update method that define in this aspx file:
<UpdateParameters>
<asp:Parameter Name="name" Type="String" />
<asp:ControlParameter ControlID="DropDownList2" Type="string"
PropertyName="SelectedValue" Name="genre" />
</UpdateParameters>
now i want to get the selected value and insert it but when i press the Update button in the row in the gridview i get this error:
Could not find control 'DropDownList2' in ControlParameter 'genre'
any idea why it happen?

Answer 1

Yes. ControlParameters only work when the DOM can find the control you're referring to that's within the same branch of the GridView. The problem is that Gridviews are a poor way of handling DOM controls because as soon as you go into a "mode" of the GridView like the EDIT mode, the entire DOM structure changes. The DOM by the way, is the Document Object Model. Because it's changed, therefore ASP cannot find the control you're referring to.
I've overcome this by doing one of two things.
First see if it works by simply tailing the control name with the '$' character.
<UpdateParameters>
<asp:Parameter Name="name" Type="String" />
<asp:ControlParameter ControlID="MyGridView$DropDownList2" Type="string"
PropertyName="SelectedValue" Name="genre" />
</UpdateParameters>
This sometimes works if you're lucky.
If not, then you'll need to find the control, get its value and pass it into the SQL parameter programmatically in code behind.
Try something like this (I use C#) ...
protected void MyGridView_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
...
GridViewRow gvRow = (GridViewRow)sender;
DropDownList myDDL = (DropDownList)gvRow.FindControl("DropDownList2");
if (myDDL != null)
{
//assuming your datasource is outside the gridview, you have to find it!
SqlDataSource sds1 = (SqlDataSource)page.FindControl("myDataSource");
if (sds1 != null)
{
sds1.UpdateParameter["genre"].DefaultValue = myDDL.SelectedValue;
... and do your databinding etc
sds1.Update();
}
}
}
I always rely on the client-side code (ASPX) to do most of the work for me, like Bind(), Eval(), etc, but over time you'll realise that to really control your program, you'll have to rely on JavaScript or code behind to do the finer bits. ASP is not always "clever" in doing what you expect it to do.